如何使用php在日历中突出显示事件日期并显示事件标题？

Question

代码：

<style>
    div.day-number   { 
        background:#999; 
        position:absolute; 
        z-index:2; 
        top:-5px; 
        right:-25px; 
        padding:5px; 
        color:#fff; 
        font-weight:bold; 
        width:20px; 
        text-align:center; 
    }
    td.calendar-day, td.calendar-day-np { 
        width:120px; 
        padding:5px 25px 5px 5px; 
        border-bottom: 1px solid #999;
        border-right: 1px solid #999;
        border-left: 1px solid #999;
        border-top: 1px solid #999;
    }
</style>
<?php
    include ('config.php');
    function draw_calendar($month, $year, $events = array())
    {
        $calendar = '<center><table cellpadding="0" cellspacing="0" class="calendar">';
        $headings = array(
            'Sunday',
            'Monday',
            'Tuesday',
            'Wednesday',
            'Thursday',
            'Friday',
            'Saturday'
        );
        $calendar.= '<tr class="calendar-row"><td class="calendar-day-head">' . implode('</td><td class="calendar-day-head">', $headings) . '</td></tr>';
        $running_day = date('w', mktime(0, 0, 0, $month, 1, $year));
        $days_in_month = date('t', mktime(0, 0, 0, $month, 1, $year));
        $days_in_this_week = 1;
        $day_counter = 0;
        $dates_array = array();
        $calendar.= '<tr class="calendar-row">';
        for ($x = 0; $x < $running_day; $x++):
            $calendar.= '<td class="calendar-day-np">&nbsp;</td>';
            $days_in_this_week++;
        endfor;
        for ($list_day = 1; $list_day <= $days_in_month; $list_day++):
            $calendar.= '<td class="calendar-day"><div style="position:relative;height:100px;">';
            $calendar.= '<div class="day-number">' . $list_day . '</div>';
            $event_day = $year . '-' . $month . '-' . $list_day;
            if (isset($events[$event_day]))
            {
                foreach($events[$event_day] as $event)
                {
                    $calendar.= '<div class="event">' . $event['title'] . '</div>';
                }
            }
            else
            {
                $calendar.= str_repeat('<p>&nbsp;</p>', 2);
            }

            $calendar.= '</div></td>';
            if ($running_day == 6):
                $calendar.= '</tr>';
                if (($day_counter + 1) != $days_in_month):
                    $calendar.= '<tr class="calendar-row">';
                endif;
                $running_day = - 1;
                $days_in_this_week = 0;
            endif;
            $days_in_this_week++;
            $running_day++;
            $day_counter++;
        endfor;
        if ($days_in_this_week < 8):
            for ($x = 1; $x <= (8 - $days_in_this_week); $x++):
                $calendar.= '<td class="calendar-day-np">&nbsp;</td>';
            endfor;
        endif;
        $calendar.= '</tr>';
        $calendar.= '</table></center>';
        $calendar = str_replace('</td>', '</td>' . "\n", $calendar);
        $calendar = str_replace('</tr>', '</tr>' . "\n", $calendar);
        return $calendar;
    }
    function random_number()
    {
        srand(time());
        return (rand() % 7);
    }
    $month = (int)($_GET['month'] ? $_GET['month'] : date('m'));
    $year = (int)($_GET['year'] ? $_GET['year'] : date('Y'));
    $select_month_control = '<select name="month" id="month">';
    for ($x = 1; $x <= 12; $x++)
    {
        $select_month_control.= '<option value="' . $x . '"' . ($x != $month ? '' : ' selected="selected"') . '>' . date('F', mktime(0, 0, 0, $x, 1, $year)) . '</option>';
    }
    $select_month_control.= '</select>';
    $year_range = 7;
    $select_year_control = '<select name="year" id="year">';
    for ($x = ($year - floor($year_range / 2)); $x <= ($year + floor($year_range / 2)); $x++)
    {
        $select_year_control.= '<option value="' . $x . '"' . ($x != $year ? '' : ' selected="selected"') . '>' . $x . '</option>';
    }
    $select_year_control.= '</select>';
    $next_month_link = '<a href="?month=' . ($month != 12 ? $month + 1 : 1) . '&year=' . ($month != 12 ? $year : $year + 1) . '" class="control">Next Month &gt;&gt;</a>';
    $previous_month_link = '<a href="?month=' . ($month != 1 ? $month - 1 : 12) . '&year=' . ($month != 1 ? $year : $year - 1) . '" class="control">&lt;&lt;    Previous Month</a>';
    $controls = '<form method="get">' . $select_month_control . $select_year_control . '&nbsp;<input type="submit" name="submit" value="Go" />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;' . $previous_month_link . '&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;' . $next_month_link . ' </form>';
    $events = array();
    $query = "SELECT title, DATE_FORMAT(date,'%Y-%m-%D') AS event_date FROM events WHERE date LIKE '$year-$month%'";
    $result = mysqli_query($db, $query);
    while ($row = mysqli_fetch_assoc($result))
        {
        $events[$row['event_date']][] = $row;
        }

    echo '<h2 style="text-align: center;">' . date('F', mktime(0, 0, 0, $month, 1, $year)) . ' ' . $year . '</h2>';
    echo '<div style="width: 30%;margin: 0 auto;">' . $controls . '</div>';
    echo '<div style="clear:both;"></div>';
    echo draw_calendar($month, $year, $events);
    echo '<br /><br />';
?>

在这段代码中，我创建了一个简单的事件生成日历。在php代码内部，我编写了一个查询，即SELECT title, DATE_FORMAT(date,'%Y-%m-%D') AS event_date FROM events WHERE date LIKE '$year-$month%'，该查询工作正常，但无法显示特定日期的事件。

下面我还提到了两个Notice错误

Notice: Undefined index: month in C:\xampp\htdocs\event_calendra\new_cal.php on line 105

Notice: Undefined index: year in C:\xampp\htdocs\event_calendra\new_cal.php on line 106

那么，如何解决此问题并在特定日期显示事件？请帮助我。

谢谢